Electronic rate means for a servo driven fuel control

ABSTRACT

This invention concerns an electronic control system suitable for controlling jet pipe temperature or rotational speed of a gas turbine engine rotor shaft. The control system is adapted to operate a solenoid which is connected to a valve in the fuel system of the engine to reduce the flow of fuel to the engine when an electrical output signal from the control system exceeds the value of a reference signal generated by the control system.

D United States Patent 1191 11 11 3,739,250 Beadman et al. 1 June 12,11973 [54] ELECTRONIC RATE MEANS FOR A SERVO 3,063,243 11/1962 Bancroft60/3928 T DRIVEN FUEL CONTROL 3,413,806 l2/l968 Belke 60/3918 3,520,1337/1970 Loft 60/3928 [75] Inventors: Terence Brockley Be man, 3,546,59812/1970 McCauley 60/3928 Ashby-de-la-Zouch, England 3,510,737 5/1970Brown et al. 318/621 X [73] Assignee: Rolls Royce Limited, Derby, P i Ei er T E, L nch England Attorney-Cushman, Darby and Cushman 221 Filed:Sept. 14, 1970 [21] Appl. No.: 71,664 [57] ABSTRACT 6 This inventionconcerns an electronic control system [30] Foreign Application PriorityData suitable for controlling jet pipe temperature or rota- Sept. 18,1969 Great Britain 46,015/69 tiohal Speed of a gas turbine engine rotorShaft- The control system is adapted to operate a solenoid which 52 us.01. 318/610, 318/621, 60/3928 T is eenheeted to a valve in the fuelSystem of the engine 51 1111. c1. G051) 11/42 to reduce the flew of fuelto the engine when an eleetri- [58] Field 61 Search 60/3928 T; 318/610,eel Output Signal from the eentrel System exceeds the 318/621 value of areference signal generated by the control system. [56] References Clted5 Claims, 2 Drawing Figures UNITED STATES PATENTS 3,478,512 11/1969Brahm 60/3928 Operafiona/ Amplifier 13mg 34 371' ltage OU/"C as? 4%] 0e24 2/ :g/MerZn/ia; a

I f .Dew'ce I I QFUP/ L J m ELECTRONIC RATE MEANS FOR A SERVO DRIVENFUEL CONTROL This invention relates to electronic control means for usein a closed-loop control system, and is particularly but not exclusivelyconcerned with electronic control means for use in a closed-loop controlsystem for controlling the jet pipe temperature of a gas turbine engine.

According to the present invention, electronic control means for use ina closed-loop control system comprises an input adapted to be connectedto receive an error signal from the system to be controlled; operationalamplifier means comprising a high gain amplifier, an input circuitconnected between said input and the input of the high gain amplifierand an output adapted to be connected to the system to be controlled;and phase-advance means connected between said input and the input ofthe high gain amplifier and adapted to supply an additional error signalto the input of the high gain amplifier when the phase-advanced errorsignal exceeds a predetermined value.

In a preferred embodiment of the invention, the phase-advance meanscomprises a phase-advance circuit and a differential switching amplifierhaving one input connected to the output of the phase-advance circuitand the other input connected to receive a fixed reference voltage.

The phase-advance means preferably also includes means for causing theadditional error signal produced thereby to rise asymptotically to afixed level when the phase-advanced error signal exceeds thepredetermined level, which means may be further arranged to cause theadditional signal to decay asymptotically when the phase-advanced errorsignal falls below the predetermined level.

Thus the output of the differential switching amplifier may be connectedto means for charging a capacitor, the voltage across the capacitorconstituting the additional error signal.

The invention also includes a closed-loop control system incorporatingelectronic control means in accordance with any of the precedingparagraphs.

Thus the closed-loop control system may be adapted to control the valueof an operating parameter, for example the jet pipe temperature and/orthe rotational speed of a compressor drive shaft of a gas turbineengine, and may comprise means for producing an electrical signaldependent upon the operating parameter and signal comparison meansconnected to receive said electrical signal and a predeterminedreference signal and adapted to produce the error signal when the valueof said electrical signal exceeds the value of the reference signal.

The system to be controlled may include a solenoid connected to theoutput of the operational amplifier means, the solenoid preferably beingincluded within the feedback loop of the operational amplifier means.

Preferably, the solenoid is operatively connected to a valve in the fuelflow system of the gas turbine engine, whereby to reduce the flow offuel to the engine when the value of said electrical signal exceeds thevalue of the reference signal.

The invention further comprises a gas turbine engine provided with aclosed-loop control system as set forth above.

The invention will now be particularly described, by way ofnon-limitative example only, with reference to the accompanyingdrawings, of which:

FIG. 1 is a schematic block diagram of a gas turbine engine providedwith a jet pipe temperature control system incorporating electroniccontrol means in accordance with the present invention; and

FIG. 2 is a circuit diagram of the electronic control means of FIG. 1. 1

The gas turbine engine shown in FIG. 1 comprises, in flow series, an airintake 10, a compressor 12, combustion equipment 14, a turbine 16drivingly connected to the compressor 12, ajet pipe 18, and a propulsionnozzle 20. Fuel is supplied to the combustion equipment 14 from a tank21 by a fuel control unit 22 which incorporates a flow reducing valve 24operated by a solenoid 26.

A temperature transducer 28 is mounted in the jet pipe 18, and producesa DC. electrical signal whose voltage is dependent upon the temperatureof the ex haust gases of the engine (T6). The output 29 of thetransducer 28 is connected to one input 30 of a comparator 32 whoseother input 34 is connected to a reference voltage source 35. When thevoltage of the signal produced by the transducer 28 exceeds thereference voltage of the source 35, i.e., when T6 exceeds its maximumpermissible value, the comparator 32 produces at its output 36 a T6error signal whose voltage is proportional to the difference betweenthese voltages. 7

The output 36 of the comparator 32 is connected to the input 37 ofelectronic control means 38 which comprises an operational amplifier 40having an input 39 connected to the input 37 and a phase advance circuit44 having an input 42 connected to the input 37. The operationalamplifier 40 comprises a high gain amplifier 46 having an input 48 andan output 50, an input circuit 52 being connected between the input 39and the input 48. The output 50 of the high gain amplifier 46constitutes the outputs of both the operational amplifier 40 and theelectronic control means 38 and is connected to energise the solenoid26. A small resistor R1 is connected between the solenoid 26 and earth,and a feedback circuit 54' is connected between the junction of theresistor R1 and the solenoid 26 and the input 48 of the high gainamplifier 46, thereby including the solenoid 26 within the feedback loopof the operational amplifier 40.

The output 56 of the phase-advance circuit 44 is con nected to one input58 of a differential switching device 60, the other input 62 of which isconnected to a reference voltage source 64. The differential switchingdevice 60 has two states, in the first of which is arranged to charge acapacitor C1 via a resistor R2 connected to a fixed voltage source 66and in the second of which it is arranged to discharge the capacitor C1via a resistor R3. The capacitor C1 is also connected, via a resistorR4, to the input 48 of the high gain amplifier 46.

In use, if the T6 error signal is increasing comparatively slowly, forexample during moderate accelerations of the engine, it is amplified inthe electronic control means 38 by the operational amplifier 40 alone soas to energise the solenoid 26. The solenoid 26 is thus graduallyenergised and causes the valve 24 to reduce the flow of fuel to thecombustion equipment 14 of the engine comparatively slowly so as toreduce T6. However, when the rate of rise of the T6 error signal exceedsa predetermined rate, for example during slam accelerations of theengine, the voltage of the output signal produced by the phase-advancecircuit 44 exceeds the voltage of the reference voltage source 64. Thiscauses the differential switching amplifier 60 to change its state,thereby charging the capacitor C1 from the fixed voltage source 66. Thevoltage across the capacitor C1 thus rises asymptotically towards thefixed voltage of the source 66 in accordance with an inverse exponentiallaw, and this asymptotically increasing voltage is applied to the input48 of the high gain amplifier 46 via R1 as an additional error signal.The solenoid 26 is therefore more rapidly energised, which causes thevalve 24 to reduce the flow of fuel to the combustion equipment 14 ofthe engine more rapidly, thus reducing T6 more rapidly.

When the rate of rise of the T6 error signal falls below thepredetermined rate, the differential switching amplifier 60 returns toits original state, causing the capacitor C1 to discharge asymptoticallyto zero in accordance with an inverse exponential law. It will beappreciated that the time constants for the charging and discharging ofC1 are not necessarily the same, and can have any suitable value.

The electronic control means 38 thus has increased gain for rapidlyrising T6 error signals and thus reduces the flow of fuel to thecombustion equipment 14 of the engine more rapidly. This minimises boththe amount by which T6 overshoots the maximum permissible value and thetotal time for which T6 exceeds the maximum permissible value, which inturn reduces thermal fatigue in the engine and increases engine life.

A typical circuit for the electronic control means 38 is shown in FIG.2. The high gain amplifier 46 comprises an integrated circuitdifferential amplifier 70 arranged to drive a simple amplifierconstituted by a transistor TRl connected in the grounded-emitterconfiguration, which is in turn connected to drive two emitterfollowerstages TR2, TR3 in cascade. The gain of the differential amplifier 70 issufficiently high for the overall gain of the operational amplifier 40to be substantially independent thereof. One input of the differentialamplifier 70 constitutes the input 48, while the other input 48a isearthed. A pair of oppositely directed diodes Dl, D2 are connected inparallel between the inputs 48, 48a so as to clamp the voltage at theinput 48 within about 0.7 volts of earth.

The differential switching device 60 also comprises an integratedcircuit differential amplifier 72, which is connected to drive anemitter-follower stage TR4 which is in turn arranged to charge thecapacitor C1 via the resistor R2. The capacitor C1 discharges throughthe resistor R3. A pair of oppositely directed diodes D3, D4 areconnected in parallel between the inputs 58, 62 so as to clamp thevoltage at the input 58 within about 0.7 volts of the voltage at theinput 62.

The phase-advance circuit 44 is of simple type and comprises a capacitorC2 and resistors R5 and R6. The input circuit 52 and the feedbackcircuit 54 of the operational amplifier 40 are composed of passiveelements and are chosen to give the operational amplifier the requiredgain and frequency response.

It will be appreciated that many modifications may be made to thedescribed electronic control means. For 65 example, the load driven bythe operational amplifier 40 need not be included within its feedbackloop, while any suitable high gain amplifier may replace the amplifier70. Also, the differential switching device could comprise adifferential amplifier arranged to drive a change-over relay.

It will also be appreciated that the electronic control means describedherein may be used in types of closedloop control system other than gasturbine engine jet pipe temperature control systems. Additionally, theelectronic control means may be used to control several parameters, forexample jet pipe temperature and the rotational speed of a compressordrive shaft, simultaneously by connecting a multi-input highest winscircuit in series with the input 30 of the comparator 32. In this caseelectrical signals dependent upon the parameters to be controlled wouldbe supplied to the respective inputs of the highest wins" circuit, onlythe higher or highest being transmitted to the output thereof. A simplehighest wins circuit comprises a plurality of diodes, one connectedbetween each input and a common resistor. The highest input forwardbiases its own diode and reverse biases the other or others.

What we claim is:

1. A gas turbine engine fuel control system including a closed loopelectronic control system comprising:

means for detecting the jet pipe temperature of the gas turbine engine,means for detecting an error between the jet pipe temperature and therequired temperature and for producing an error signal dependentthereon,

means for adjusting the fuel supply system to the engine to reduce saiderror,

an input adapted for connection to receive said error signal,

operational amplifier means comprising a high gain amplifier,

an input circuit connected between said input and the input of the highgain amplifier and an output adapted for connection to the means foradjusting the fuel supply,

phase advance means connected between said input and the input of thehigh gain amplifier and adapted to supply an additional error signalwith the first mentioned error signal, to the input of the high gainamplifier when the phase advanced error signal exceeds a predeterminedvalue,

the phase advance means comprising,

a phase advance circuit, and

a differential switching amplifier having one input connected to theoutput of the phase-advance circuit and the gher input connected toreceive a fixed reference voltage,

the output of the differential switching amplifier being connected tomeans for charging a capacitor, the voltage across the capacitorconstituting the additional error signal,

the phase advance means causing the additional error signal to riseasymptotically to a fixed level when the phase advance error signalexceeds the predetermined value and to decay asymptotically when thephase advance error signal falls below the predetermined value.

2. A gas turbine engine fuel control system as claimed in claim 1,comprising:

means for detecting an error signal between the jet pipe temperature andthe required temperatures, including, and

claimed in claim 3, wherein the solenoid is included within the feedbackloop of the operational amplifier means.

5. A gas turbine engine fuel control system as claimed in claim 4,wherein the solenoid is operatively connected to a valve in the fuelflow system of the gas turbine engine, whereby to reduce the flow offuel to the engine when the value of said electrical signal exceeds thevalue of the reference signal.

1. A gas turbine engine fuel control system including a closed loopelectronic control system comprising: means for detecting the jet pipetemperature of the gas turbine engine, means for detecting an errorbetween the jet pipe temperature and the required temperature and forproducing an error signal dependent thereon, means for adjusting thefuel supply system to the engine to reduce said error, an input adaptedfor connection to receive said error signal, operational amplifier meanscomprising a high gain amplifier, an input circuit connected betweensaid input and the input of the high gain amplifier and an outputadapted for connection to the means for adjusting the fuel supply, phaseadvance means connected between said input and the input of the highgain amplifier and adapted to supply an additional error signal with thefirst mentioned error signal, to the input of the high gain amplifierwhen the phase advanced error signal exceeds a predetermined value, thephase advance means comprising, a phase advance circuit, and adifferential switching amplifier having one input connected to theoutput of the phase-advance circuit and the gher input connected toreceive a fixed reference voltage, the output of the differentialswitching amplifier being connected to means for charging a capacitor,the voltage across the capacitor constituting the additional errorsignal, the phase advance means causing the additional error signal torise asymptotically to a fixed level when the phase advance error signalexceeds the predetermined value and to decay asymptotically when thephase advance error signal falls below the predetermined value.
 2. A gasturbine engine fuel control system as claimed in claim 1, comprising:means for detecting an error signal between the jet pipe temperature andthe required temperatures, including, and signal comparison meansconnected to receive an electrical signal from the means for detectingthe jet pipe temperature and a predetermined reference signal andadapted to produce the error signal when the value of said electricalsignal exceeds the value of the reference signal.
 3. A gas turbineengine fuel control system as in claim 1 wherein the system includes asolenoid connected to the output of the operational amplifier means. 4.A gas turbine engine fuel control system as claimed in claim 3, whereinthe solenoid is included within the feedback loop of the operationalamplifier means.
 5. A gas turbine engine fuel control system as claimedin claim 4, wherein the solenoid is operatively connected to a valve inthe fuel flow system of the gas turbine engine, whereby to reduce theflow of fuel to the engine when the value of said electrical signalexceeds the value of the reference signal.